Multi-cylinder double-acting stirling cycle engines

ABSTRACT

In a Stirling cycle engine, a piston is provided with an internal cavity having a volume greater than the swept volume of the cylinder and a passage connecting into the cavity from a space located in a position between two piston rings about the piston. A groove about each of the two piston rings works as nonreturn valves ensuring minimum cycle pressure inside the piston cavity.

Umted States Patent 1191 [111 3,927,529 Hakansson 5] Dec. 23, 1975 MULTI-CYLINDER DOUBLE-ACTING 3,546,877 12/1970 Beukering et al 60/521 x STIRLING CYCLE ENGINES 3,733,837 5/1973 Lobb 60/522 x 3,793,836 2/1974 Abrahams 60/521 [75] Inventor: Sven Anders Samuel Hakansson,

Varberg, Sweden [73] Assignee: Kommanditbolaget United Stirling (Sweden) AB & Co., Malmo, Sweden [22] Filed: July 31, 1974 [21] App]. No.: 493,390

[30] Foreign Application Priority Data Aug. 22, 1973 United Kingdom ..-39694 [52] US. Cl. 60/521 [51] Int. Cl. F01B 29/10 [58] Field of Search 60/521, 522, 524

[56] References Cited UNITED STATES PATENTS 3,364,675 l/l968 Dorer 60/522 Primary ExaminerMartin P. Schwadron Assistant Examiner-H. Burks, Jr. Attorney, Agent, or Firm-Laurence R. Brown [57] ABSTRACT In' a Stirling cycle engine, a piston is provided with an internal cavity having a volume greater than the swept volume of the cylinder and a passage connecting into the cavity from a space located in a position between two piston rings about the piston. A groove about each of the two piston rings works as non-return valves ensuring minimum cycle'pressure inside the piston cavity.

2 Claims, 2 Drawing Figures US. Patent Dec. 23, 1975 3,927,529

Fig.1

I ,VI IIII Fig.2

MULTI-CYLINDER DOUBLE-ACTING STIRLING CYCLE ENGINES This invention relates to a multi-cylinder doubleacting Stirling cycle engine of the kind (herein called the kind defined) in which each cylinder contains a piston which separates a low-temperature working space from a high temperature working space in the cylinder and each piston separates from each other two different charges of workin g gas operating in respective working cycles. each piston having at least two axially spaced piston rings.

If some working gas leaks past one of the pistons it may occur that during the working cycles of one of the working gas charges the mean effective pressure is higher than that obtained during the cycles of the other working gas charges. A higher mean effective pressure results in a higher output from one or more of the cylinders, and thus there is an uneven power distribution among the cylinders of the engine. For reasons of safety the governing of the engine total power output must be based upon the output from that one of the engine cylinders having the largest power output, and consequently an uneven power distribution will result in a decrease of the total output of the engine.

It has previously been proposed to provide an engine of the kind defined with a special equalizing valve ensuring that all working gas charges in the engine will operate at the same mean pressure. However, such valve will make the engine more expensive and its use will cause a loss in power.

Therefore it is an object of the present invention to avoid the occurrence of different mean effective pressures in the separate working gas charges of an engine of the kind defined.

According to the present invention there is provided an engine of the kind defined wherein each piston is provided with a cavity havinga volume greater than the swept volume of the cylinder and with at least one passage connecting said cavity at the outer surface of the piston to a space between said two piston rings.

The said space will be of very small volume if, as is usual, the periphery of the piston is very close to the cylinder wall.

How the invention may be put into practice is described in more detail with reference to the accompanying drawing, in which:

FIG. 1 schematically shows a known type of Stirling engine, and

FIG. 2 shows to a larger scale a part of an engine according to the present invention.

The engine shown in FIG. 1 is of the kind defined and comprises four cylinders 1 or 2 or 3 or 4 each accommodating a reciprocating respective piston 5 or 6 or 7 or 8 provided with a respective piston rod 9 or 10 or 1 1 or 12.

Each piston 5 or 6 or 7 or 8 divides the respective cylinder 1 or 2 or 3 or 4 in which it is arranged into two chambers of variable volumes an upper chamber and a lower chamber. The upper chamber 13 of the cylinder 2 is connected with the lower chamber 14 of the cylinder 1. Similarly the upper chamber 15, 17 and 19 of the cylinders 3, 4 and 1 are connected with the lower chambers 16, 18 and 20 of the cylinders 2, 3 and 4 respectively. The connections are established through pipes and units 21 or 22 or 23 or 24 each including a regenerator and a cooler. The upper chambers 13, 15, 17 and 19 are heated by heating devices 2 (not shown) and are thus kept at a high temperature level. The lower chambers 14, l6, l8 and 20 .are kept at a low temperature level due to the coolers in the units 21 or 22 or 23 or 24.

The volume variations of each of the upper chambers at the high temperature level are synchronous with but phased degrees in advance of the volume variations of the lower chamber with which it is connected. The engine shown will contain four separate working gas charges, the separation being effected by the pistons. The working gas is hydrogen or helium at a high pressure which during operation will vary, for example, between 225 and bars.

The lower chambers 14, 16, 18, 20 are connected to a pipe 25 through a passage containing a non-return valve allowing flow of gas only in the direction into the respective lower chamber. In the drawing only the non-return valve 26 between the chamber 20 and the pipe 25 has a reference numeral. The lower chambers l4, 16, 18 and 20 are also connected to individual pipes 27, 28, 29 and 30 respectively through non-return valves allowing flow of gas only in the direction out of the lower chambers. Only the valve 31 governing the passage between the chamber 20 and the pipe 30 has a reference numeral.

During operation the pressure prevailing in the pipe 25 is the minimum working cycle pressure which occurs in the lower chambers 14 and 16 and 18 and 20, whereas the pressure prevailing in the pipe 27-28-29-30 is the maximum working cycle pressure which occurs in the said lower chambers.

A valve 32 may be used for supplying gas to the engine from a source not shown. A valve 33 may be used for dumping gas from the engine into a reservoir or to atmosphere.

FIG. 2 shows one of the cylinders and its piston to a larger scale and in more detail. The piston in FIG. 2 comprises a bottom part 34 connected to a piston rod 35 and a dome 36 enclosing a cavity 37 having a volume exceeding the swept volume of the cylinder. Two piston rings 38 and 39 are axially spaced and with the piston serve to seal the upper part of the cylinder from the lower part of the cylinder. Several bores 40 (two of which are shown) connect the cavity 37 with the space limited by the two piston rings 38 and 39 and the walls of the piston and the cylinder.

A groove 41 is provided at the upper side of the annular recess receiving the piston ring 38. Likewise a groove 42 is provided at the lower side of the annular recess receiving the piston ring 39.

An engine of the kind defined with piston arrangements as described with reference to FIG. 2 will operate as follows:

During normal operation under constant load the gas pressure will vary between equal levels in the four separate working gas charges respectively contained mainly in the chambers 19-20, 13-14, 15-16 and 17-18. Therefore the non-return valves will not operate at all, and the minimum gas pressure will prevail in the pipe 25 while equal maximum pressures will prevail in the four pipes 27-30.

Together with the adjacent piston rings 38 and 39, the two grooves 41 and 42 will act as non-return valves ensuring that minimum cycle pressure prevails inside the dome 36. If one of the rings 38 or 39 allows Q leak of gas into the cavity 37 in the dome the same Piston ring will allow flow of gas from the interior of the dome (now containing gas at a somewhat higher pr1ure) back into the working charge during the following piston stroke.

What is claimed is:

1. A multi-cylinder double-acting Stirling cycle engine of the kind in which each cylinder contains a piston which separates a low temperature working space from a high temperature working space in the cylinder and each piston separates from each other two different charges of working gas operating in respective working cycles by means of at least two axially spaced piston rings and having working gas conveyance means connected to each said cylinder with working gas therein maintained at minimum cycle pressure, characterized in that each piston is provided with a cavity having a volume greater than the swept volume of the cylinder for receiving therein said working gas that may leak through one of said piston rings into the space between said two piston rings, at least one passage defined in said piston connecting said cavity at the outer surface of the piston to the space between said two piston rings thereby to permit entry of leakage gas into said cavity, and means permitting passage of working gas from said space between said two piston rings into said two charges for thereby maintaining said minimum cycle pressure in said cavity.

2. A Stirling cycle engine as claimed in claim 1, characterized in that said two piston rings co-operate with their adjacent recess wall parts to act as non-return valves allowing flow of gas only in the direction from said cavity to constitute said last mentioned means. 

1. A multi-cylinder double-acting Stirling cycle engine of the kind in which each cylinder contains a piston which separates a low temperature working space from a high temperature working space in the cylinder and each piston separates from each other two different Charges of working gas operating in respective working cycles by means of at least two axially spaced piston rings and having working gas conveyance means connected to each said cylinder with working gas therein maintained at minimum cycle pressure, characterized in that each piston is provided with a cavity having a volume greater than the swept volume of the cylinder for receiving therein said working gas that may leak through one of said piston rings into the space between said two piston rings, at least one passage defined in said piston connecting said cavity at the outer surface of the piston to the space between said two piston rings thereby to permit entry of leakage gas into said cavity, and means permitting passage of working gas from said space between said two piston rings into said two charges for thereby maintaining said minimum cycle pressure in said cavity.
 2. A Stirling cycle engine as claimed in claim 1, characterized in that said two piston rings co-operate with their adjacent recess wall parts to act as non-return valves allowing flow of gas only in the direction from said cavity to constitute said last mentioned means. 